In the past, an air bag unit has been used for protecting an occupant in a vehicle from the secondary collision (i.e. collision of the body of the occupant against car body by inertia), and such air bag unit is installed on the fixed portion of car body such as console box in front of the seat or on the back of the seat, or on the central portion of the steering wheel in front of the driver's seat.
This air bag unit is provided with an inflator with blowing holes, from which gas is blown out at the collision, and the air bag folded to cover the blowing holes is accommodated together with said inflator in a cover member, called module cover, which can be broken and developed in an emergency.
Such conventional type air bag unit is disclosed in the Japanese Unscreened Utility Model Publication No. 123355/1988. FIG. 7 shows an air bag unit disclosed in this publication.
As shown in FIG. 7, the air bag unit 1 comprises a gas generator 2, which is operated at the vehicle collision, generates gas and blows out the gas from the blowing holes 4 toward the direction perpendicular to the direction of the occupant, and a bag 5, the base 5a of which is fixed by a ring member 3 on the gas generator 2 as if it encloses said blowing holes 4 and which is inflated and expanded by the gas from said gas generator 2. Further, a lateral wall 3a facing the blowing holes 4 of said gas generator 2 is furnished on the side of said ring member 3.
In the air bag unit 1 with such arrangement, no thermal influence is exerted on the bag 5 and its strength can be maintained even when high temperature gas is continuously blown out from the gas generator 2 because the base 5a of the bag 5 is protected by the lateral wall 3a from the exposure to hot gas.
In the meantime, in the conventional type air bag unit 1 as described above, it is necessary to provide a lateral wall 3a facing to the blowing holes 4 of said gas generator 2 on the side of the ring member 3 for the purpose of protecting the base 5a of the bag 5 from hot gas.
The air bag unit for the driver is to be installed on the steering wheel in order to avoid the secondary collision of the occupant, e.g. the driver. When the above air bag unit is installed on the steering wheel, inertial weight is increased due to the ring member 3, and this leads to the decrease in the driving stability. Also, there is a problem that the unit must be larger because the ring member 3 must be furnished.
Further, there are the demands to reduce the cost and to increase the reliability by reducing the number of the component parts, while this could not be attained in the above air bag unit as described above.
To solve the above problems, the object of the present invention is to offer an air bag unit, which can be provided in compact and lightweight design and which can minimize the number of the component parts.